Automatic Position Reporting System

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Automatic Packet Reporting System (APRS) is an amateur radio based automatic packet reporting system for tracking and digital communications, and was developed by Bob Bruninga, callsign WB4APR, at the United States Naval Academy.

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[edit] Capabilities

In its simplest implementation, APRS is used to transmit real-time reports of the exact location of a person or object via a data signal sent over amateur radio frequencies. In addition to real-time position reporting capabilities using attached Global Positioning System receivers, APRS is also capable of transmitting a wide variety of data, including weather reports, short text messages, radio direction finding bearings, telemetry data, and storm forecasts. Once transmitted, these reports can be combined with a computer and mapping software to show the transmitted data superimposed with great precision upon a map display.

[edit] Technical Information

In its most widely used form, APRS is transported over the AX.25 protocol using 1200 baud Bell 202 audio frequency-shift keying on frequencies located within the amateur 2-meter band:

An extensive digital repeater, or "digipeater" network provides transport for APRS packets on these frequencies. Internet gateway stations (i-Gates) connect the on-air APRS network to the APRS Internet System (APRS-IS), which serves as a worldwide, high-bandwidth backbone for APRS data. Stations can tap into this stream directly, and a number of databases connected to the APRS-IS allow web-based access to the data as well as more advanced data mining capabilities. A number of low-earth orbiting satellites and the International Space Station are capable of relaying APRS data.

[edit] Equipment Settings

An APRS infrastructure is comprised of a variety of Terminal Node Controller (TNC) equipment put in place by individual Amateur Radio operators. This includes soundcards interfacing a radio to a computer, simple TNC's, and "smart" TNC's. The "smart" TNC's are capable of determining what has already happened with the packet (unit of information) and can prevent redundant packet repeating within the network.

There are a few radios on the market which include a built-in AX.25 Terminal Node Controller and APRS software, and are capable of working with or without the need for an external GPS device. Two common models are the mobile Kenwood TM-D700A, and the handheld Kenwood TH-D7AG.

Reporting stations use a method of routing called a "path" to broadcast the information through a network. In a typical packet network, a station would use a path of known stations such as "via n8xxx,n8yyy." This causes the packet to be repeated through the two stations before it stops. In APRS, generic callsigns are assigned to repeater stations to allow a more automatic operation.

RECOMMENDED PATH: Throughout North America (and in many other regions) the recommended path for Mobiles or portable stations is now WIDE1-1,WIDE2-1. Fixed Stations (Homes, etc.) should normally use plain WIDE2-2 or less.

OLD PATH: Early on, the widely accepted method of configuring stations was to enable the short-range stations to repeat packets requesting a path of "RELAY" and long-range stations were configured to repeat both "RELAY" and "WIDE" packets. This was accomplished by setting the station's MYALIAS setting to RELAY or WIDE as needed. This resulted in a path of RELAY,WIDE for reporting stations. However, there was no duplicate packet checking or alias substitution. This sometimes caused beacons to "ping pong" back and forth instead of propagating outwards from the source. This caused lots of interference. With no alias substitution, you couldn't tell which digipeaters a beacon had used.

NEW PATH: With the advent of the new "smart" TNC's, the stations that used to be "WIDE" are now "WIDEn-N." This means a packet with a path of WIDE2-2 would be repeated through the first station as WIDE2-2, but the path will be modified (decremented) to WIDE2-1 for the next station to repeat. The packet stops being repeated when the "-N" portion of the path reaches "-0." This new protocol has caused the RELAY, WIDE path to become obsolete. Users are being asked to configure "RELAY" stations as WIDE1-1. This results in a new, more efficient path of WIDE1-1,WIDE2-1.

[edit] History

Bob Bruninga implemented the earliest ancestor of APRS on an Apple II computer in 1982. This early version was used to map high frequency Navy position reports. In 1984, Bruninga developed a more advanced version on a Commodore VIC-20 for reporting the position and status of horses in a 100-mile endurance run. During the next two years, Bruninga continued to develop the system, which he now called the Connectionless Emergency Traffic System (CETS). Following a series of FEMA exercises using CETS, the system was ported to the IBM PC. During the early 1990s, CETS, now known as the Automatic Packet Reporting System, continued to evolve into its current form. As GPS technology became more widely available, 'Packet' was replaced with 'Position' to better describe the most common use of the system.

[edit] Related systems

The APRS protocol has been adapted and extended to support projects not directly related to its original purpose. The most notable of these are the FireNet and PropNET projects.

APRS FireNet is an Internet-based system using the APRS protocol and much of the same client software to provide fire fighting, earthquake, and weather information in much higher volume and detail than the traditional APRS system is capable of carrying.

PropNET uses the APRS protocol over AX.25 and PSK31 to study radio frequency propagation. PropNET 'probes' transmit position reports, along with information on transmitter power, elevation, and antenna gain, at various frequencies to allow monitoring stations to detect changes in propagation conditions.

Open Trac was created to provide an alternative to APRS that was cleaner and more functional than APRS.

[edit] See also

[edit] External links

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